GG = 6.6740831 * 10 ^ (-11)
M = 5.9722 * 10 ^ 24
R1 = 6.378 * 10 ^ 6
m2 = 1
F1 = GG * M * m2 / R1 ^ 2
MsgBox F1

R2 = R1 + 21000
F2 = GG * M * m2 / R2 ^ 2
MsgBox F2

differenceInWeights = Abs(F1 - F2)

MsgBox differenceInWeights